The development of the integrated circuit (IC) has been one of the most significant technical advances in the twentieth century. Furthermore, continuing research and development has produced successive significant advances. In application, several integrated circuits are often combined on a single circuit board to form electronic systems. Further, such circuit boards are also connected together electrically to form complex electronic systems/apparatus. The use of such circuit boards is advantageous in that they may be conveniently replaced when one or more of the individual ICs on the board degrades or fails.
The advances of integrated circuit technology, however, have brought the challenge of quality control and circuit repair. This requires apparatus and methods which are specially adapted for testing the operating condition of electronic circuits which include individual ICs, as well as other circuit elements, both active and passive, which are connected to the ICs.
The importance of quality control is self-evident, as the replacement of inoperative boards due to IC failure is expensive, as well as requiring substantial valuable time of trained personnel. Prompt and accurate repair of circuit boards is also becoming increasingly important, again due to the cost of repair time, as well as the large number of expensive circuit boards.
One significant difficulty in the repair of circuit boards is that a board may be rendered inoperative by the failure of a portion of an IC or just one or more other circuit components, which may be difficult to locate, particularly in-circuit. A large number of circuit nodes, including the individual pin connections of the ICs, typically must be tested to identify the circuit faults.
Apparatus for testing integrated circuits is known, and insofar as they are designed to provide an automatic sequential interrogation of the individual pin connections of an IC under test without operator intervention, such apparatus is referred to as automatic test equipment (ATE). However, such equipment, which is available from only a few manufacturers, have the significant limitations of being expensive and quite sophisticated in operation (usually also including sophisticated software), as well as requiring a trained operator. Further, even such expensive and sophisticated equipment have proven to be somewhat unreliable with respect to accurately ascertaining the condition of the circuit under test and identifying its faults.
As an alternative to expensive and sophisticated ATE, relatively inexpensive semiconductor testers have been developed which have proven to be extremely useful for an individual technician who is involved in the repair or "troubleshooting" of integrated circuits and other semiconductor devices. Such apparatus is disclosed in U. S. Pat. No. 3,973,198, issued on Aug. 3, 1976 in the name of Bill Hunt, and U.S. Pat. No. 4,074,195, issued on Feb. 14, 1978, also in the name of Bill Hunt, both of which are owned by the assignee of the present invention.
The apparatus described in the above two patents includes circuitry which obtains an analog "signature" representating the operating condition of individual semiconductor junctions when the junction is in-circuit. The analog signature is displayed on a CRT, which is typically an integral part of the apparatus. A trained operator can interpret the signature to identify failed junctions or components. The relatively low cost of the apparatus permits its purchase in large numbers by organizations having large repair facilities as well as by individual technicians.
However, a significant disadvantage of such an instrument in some instances, such as in the testing of ICs, is that the testing must be done manually, i.e. pin-by-pin. The operator is at least required to inspect the displayed signature of each pin of the IC under test and in some cases must manipulate test leads or switching equipment manually for each IC pin connection.
Testing of circuit boards which include a number of ICs is thus quite slow with such apparatus, which may in effect preclude the use of such apparatus in many applications, including quality control, even though the information that may be obtained about the condition of the ICs and other circuit components by use of the apparatus is more complete and reliable than that obtained by much more expensive and sophisticated test equipment. Another disadvantage is that such apparatus typically does require a trained operator, who must examine the signature of each junction and make a judgment as to whether it is satisfactory.
Thus, there is a need for test equipment which is substantially as fast as, but less expensive than, existing ATE and which reliably and accurately tests integrated circuits and other elements in electronic circuits, including identifying those circuit nodes in the electronic circuit having signatures which are sufficiently different than normal to merit further evaluation.